The present invention relates to a ball valve adapted to be inserted into a pipe line system for the purposes such as opening and closure, and change-over of a flow path. It should be noted that the term "flow path" as used herein includes both the path of pressurized liquid and the path of high pressure gas such as steam.
It is most important that ball valves employed in such applications remain leak-free though in use for many years in a high pressure liquid or gas flowing environment, and that they always provide easy and rapid operation. Various improvements have been proposed to satisfy these requirements, and these improvements have often been directed to the arrangement for the sealing and intercepting effect desired between a movable component located in the flow path and a stationary component enclosing the movable component. More specifically, various improvements have been directed to effective maintenance of liquid- or gas-tightness in the intercepting arrangement, and a high wearing resistance of the movable component which may be repeatedly operated.
Generally, the movable component in a ball valve is a valve body shaped substantially in a sphere, and the stationary component is an outer casing adapted to enclose the movable component. Accordingly, intercepting surfaces between the substantially spheric valve body and the outer casing enclosing the valve body must be maintained in close contact with high precision. This is especially true in a ball valve employed in a high pressure environment wherein the valve body serving as the movable component is also influenced by the high pressure, and the operation of the valve body under such a high pressure imposes a high frictional pressure particularly to the surface of the valve body which is in contact with the outer casing. To overcome such a frictional pressure, there has recently been provided an annular sealing member serving as a valve seat. The annular sealing member is formed of a high molecular weight plastic such as Teflon, and it is interposed between the movable valve body and the stationary outer casing so as to provide a resistance to possible wearing due to the operation of the movable valve body.
Even with such an improvement, however, the sealing member may be subjected to so-called plastic flow depending on the frequency at which the valve body is operated or to the deformation and distortion due to wearing, resulting in deterioration of the interception. The annular sealing member interposed between the movable valve body and the stationary outer casing has its surface in contact with the valve body and rubs against the valve body as the latter is rotated. The valve body is formed at this particular portion as an accurate convexo-spherical surface, and the portion of the sealing member being in contact with this convexo-spherical surface is formed as an accurate concavo-spherical surface to maintain the desired intercepting effect at a high level. However, leakage cannot be reliably prevented by only the foregoing measure unless a sufficient contact pressure is exerted upon the rubbing surface. The accurate form required for the rubbing surface would be deformed due to wearing caused by repeated operation of the valve unless the contact pressure exerted upon the rubbing surface may respond at every portion to the deformation.
In one of the most recently developed ball valves, it has been proposed that the annular sealing member serving as the valve seat include a cylindrical outer periphery, a concavo-spherical inner surface and an annular groove extending therebetween. In this structure, the cylindric outer periphery bears against the inner surface of the stationary outer casing, and the concavo-spheric inner surface is in slidable contact with the outer surface of the movable valve body. The annular sealing member has a generally V-shaped, radial cross-section, and the concavo-spheric inner surface is saucer shaped.
Specifically, it has been proposed that a biasing pressure extending in the directions in which the annular groove is transversely contracted be exerted on the cylindric outer periphery and concavo-spherical inner edge in assembling the ball valve so that a force counteracting the potential pressure may urge the sealing member against the movable valve body. Additionally, a fluid pressure in the flow path is positively introduced into the annular groove so that the concavo-spherical surface in the form of a saucer is brought into close contact with the convexo-spherical surface of the valve body.
The foregoing biasing pressure for maintenance of close contact has been found to result in an unreasonably large force of operation since the counteracting force is provided by a tightening force in assembling the valve and such a tightening force increases not only a degree of close contact but also a frictional force. Thus, the tightening force to be used in assembling the ball valve is limited. Similarly, the use of fluid pressure within the annular groove to urge the concavo-spherical inner surface against the valve body from the rear side of the inner surface and simultaneously to urge the cylindrical outer periphery against the outer casing from the rear side of the outer periphery may provide the desired effect but only under the fluid pressure in excess of a certain limit which overcomes the rigidity determined by the material and the thickness of the sealing member itself. A ball valve employing such a measure will be effective as a ball valve adapted for a high pressure but clearly disadvantageous in the aspect of versatility.
In larger diameter pipe line systems employing comparably sized ball valves to control fluid flow in the system, the valve body serving as a movable component will be correspondingly bulky and heavy. Wearing on the surfaces along which the movable valve body and the sealing member are in slidable contact with each other is rather significantly influenced by the load of the movable valve body in practice, but this influence has been heretofore substantially neglected.
The first object of the present invention is to improve the sealing and intercepting effect between the movable valve body and the stationary outer casing so that this effect may be obtained regardless of the pressure within the flow path. The second object of the present invention is to provide an arrangement such that the sealing member interposed between the movable valve body and the stationary outer casing provides a reliable sealing and intercepting effect not only along its surface which bears against the outer casing but also its surface which rubs against the movable valve body regardless of the frequency at which the valve is operated, particularly providing the urging effect immediately in response to deformation and distortion thereof. The third object of the present invention is to prevent undesirable wearing occurring on the intercepting surface due to a load of the movable valve body with which a lower portion of the sealing member is concentratedly burdened so that the rubbing surface may be evenly urged in terms of condition so as to provide a permanently reliable sealing and intercepting effect. The other objects of the present invention will be apparent from the following description of features and preferred embodiment of the present invention.